i8o OUR HOUSEHOLD INSECTS 



extremely minute hairs distributed all over its surface, 

 but very evenly and regularly disposed. There are also 

 larger hairs on the nervures, which may perhaps be 

 sensory in function. 



The wings can be vibrated with marvellous rapidity, 

 sufficiently so to produce a recognisable musical note. 

 Attempts have been made to determine the number of 

 vibrations per second by observing the pitch of the note. 

 The usual pitch of a fly's hum is somewhere about the 

 notes E or F, and the corresponding number of vibrations 

 would b$ something between 320 and 350. The charac- 

 teristic buzzing of our bluebottle, however, is not due 

 to the vibration of the wings, nor, like the shrill song of 

 the grasshopper, or the squeak of the water- beetle, to 

 the friction of one part of the body against another j for 

 Landois discovered that the thorax of a bluebottle con- 

 tinued to buzz with scarcely diminished vigour after the 

 separation of the wings, legs, head, and abdomen. There 

 is also a large and beautiful yellow - banded fly, called 

 Sericomyia borealis, not uncommon in our mountainous 

 districts, which has by several observers been noticed to 

 "sing" whilst at rest. The Rev. J. Hellins, of Exeter, 

 thus writes of it in December 1881: " One day during 

 the past autumn I went with a small party for a walk 

 on Dartmoor, near Okehampton. After some miles of 

 rough tramp up and down several tors, as the afternoon 

 was drawing on, we found ourselves on a heap of stones 

 on the top of Cawsand, and were glad to rest there 

 awhile. Before long, a piping sound was audible, and one 

 of the party said the wind was whistling; but to this 

 explanation I demurred, having some recollection of 

 having heard the noise before ; so, looking round, I soon 

 saw several large flies resting on the stones, and was 

 presently able to convince my friend that the sound 



